Minimizing Optical Aberrations – Focus on Seidel or Zernike
Minimizing Optical Aberrations is the end goal of any lens system design. Lens aberrations are normally defects in the design of the lens or lens system. They are not necessarily material or manufacturing defects. They can be. However, optical aberrations are frequently the result of a non-optimized design. They can be simply the shape, curvature, or the placement of a lens in a complex lens system.
A mathematically rugged optimization scheme is one secret to eliminating optical aberrations.
Your choice of optimization goals, even your priority of goals, can make or break your optical design.
reTORT ray tracer v2.0.27 offers the most rugged optimization schemes on the market today. And you will find the most flexibility in optimization goals. Not only that, you even have your choice of whether to use Seidel or Zernike functions. And, reTORT calculates each of these directly. One is not derived from the other. Whichever suits your purpose, you get the most accurate computations with reTORT v2.0.27.
Whether Seidel or Zernike, each of these has its place and its following among optical designers. We’ll address some of the issues involved in minimizing optical aberrations below.
Optical Aberrations
The six common optical aberration components are below. You may have heard of seven primary aberrations. Or, you may know them by different names. But these will suffice for our purposes.
- Astigmatism
- Spherical Aberration
- Chromatic Aberration
- Field Curvature
- Distortion
- Coma
A lens collects light and ideally focuses it at a single point. Instead, due to these aberration components, the lens produces a blur circle. Our objective is to minimize or eliminate this blur circle. Try reTORT. You will find reTORT gives you the tools to minimize optical aberrations effectively and quickly. Our job in providing you with reTORT is to make this easy and accurate.
Design to Minimize Optical Aberrations
You often optimize lens systems by targeting resolution metrics such as spot size or MTF. You may also target aberrations such as wavefront error or a particular aberration component. reTORT offers the ability to optimize lens systems for any of these goals.
We do not recommend you begin by optimizing for minimal wavefront error. This can make the optimization search space difficult to navigate. Instead, it may point you to a near optimum. You may not even be close to your correct solution.
reTORT can correct all common aberrations as well as higher order terms. As an example, by using the Seidel aberration result table in reTORT, the optical designer can figure out which lenses are introducing the most aberration. In this way, you, the optical designer, can add corrective lenses in problem areas. Or it may lead you to remove lenses where there is too much glass, reducing size and weight.
Your ability in reTORT to view a table of per-surface aberrations is a powerful tool. Your ability to understand which surfaces in their lens system are likely to be introducing the most wavefront error supports a superior workflow in optical lens design.
In this way, you can use reTORT to provide a solid basis for iterative, low-aberration lens design. Actually, after this iterative workflow, systems that are already focusing quite well often benefit the most from optimizing for minimal wavefront error.
Our convenient wizard interface now fully supports the entire optimization process. This allows you to tweak your design based on either spot size or wavefront error at every step of the design process.
But There’s More
You have several other tools in reTORT to help diagnose optical aberrations. The TRA Trace plot (also known as the “Ray Fan” plot) shows the designer where in the image plane a merdonial or sagittal fan of rays falls with respect to its location in the entrance pupil.
The Wavefront Error Plot helps an optical designer visualize the optical path difference for a set of rays that begin at a specific object point and converge to a focal point in the image plane.
These plots and data tables, along with a powerful optimizer, are the best tools for an optical designer to use when reducing aberrations in a modern optical system.
Seidel Versus Zernike
Is there a reason to make a choice?
Not really, it often depends with which you are most comfortable.
Some optical designers prefer the mathematic elegancy of Zernike. Whereas Seidel often has a more immediately meaningful definition. You may find this allows them to be easily understood and useful due to their simplicity
So, reTORT provides you the ability to choose either as an optimization goal. And we don’t derive one from the other. Both Seidel and Zernike functions are computed directly for best accuracy.
reTORT ray tracer 2.0.27 provides you the optimal design experience with:
- Quick and easy wizards to set up your optimization scheme.
- Native gradient index and metasurface definitions and computations, no need for added libraries or adjustments.
- A wide choice of directly calculated optimization targets.
- The ability to set index of refraction bounds to yield a manufacturable design.
- The ultimate tools to use the most advanced methods available to reduce size and weight while maximizing performance.
